The quantum theory reveals the wave-particle duality of light. In view of wave and particle both having momentum, an object may gain kinetic energy when light directly illuminates the object that reflects according to the momentum theorem.
In recent years, solar sails have been a hot subject of future deep-space exploration spacecraft. Operating as outer space devices without carrying propellant, solar sails use light pressure as their main power source. Moreover, with the increasing development of vacuum experimental technologies, the test for simulating space environments in ground laboratory has matured. Therefore, it is important to calibrate and measure light pressure exerted on and “felt” by the objects. Due to the non-perfect reflection, the measured pressure is a slight reduction in laboratory vacuum environments. But the light pressure “felt” by the objects is important to provide guidance for the design and control of solar sails.
Since the magnitude of light pressure is very small, it is impossible to measure and calibrate light pressure with conventional force measuring devices and calibrating devices.
Π. H. Lebedev, who is the first person in history to relatively accurately measure light pressure, adopted a winglet fastened to a glass fiber to measure the light pressure. The light pressure acts on the winglet and thus makes the glass fiber twist, and then the light pressure can be worked out by measuring the value of torsion angle of the glass fiber.
Chinese patent publication No. CN 102322951A discloses a method for working out light pressure values from the micro displacements of mirrors illuminated by light. It is necessary in this method to use shock absorption elements, optical fiber displacement sensors, and capacitive displacement sensors, and thus the structural composition for implementing this method is very complicated.
Chinese patent publication No. CN 102252753A discloses a method for detecting infrared radiation with a cantilever resonant structure. It is necessary in this method to use the resonant structure manufactured with micro-nano processing techniques which is relatively complex and the dynamic response sensitivity of the cantilever is relatively low.
Chinese patent publication No. CN 103728017A discloses a method for calculating light pressure from the intensity and frequency of interference light formed by coupling the reflected light and the modulated light based on the vibration of the nano silver film illuminated by light. It is necessary in this method to generate the interference light with a fiber coupler, and demodulate the interference light with an optical phase demodulation device, and thus the structural composition for implementing this method is also very complex.
Furthermore, other devices for measuring light pressure mainly include thermopiles or piezoelectric multiplier tubes. The working principle of thermopile is to convert thermal energy into electrical energy, and output voltage correlate linearly to the value of the local temperature gradient. Thus, the light intensity could be calculated in turn, and then calculate the light pressure in accordance with the intensity-pressure relationship of light P=I/c revealed by the special theory of relativity, wherein, P is light pressure, I is light intensity and c is the speed of light. The main principle of photomultiplier tube is to amplify the current created by light illumination hundredfold with the aid of photoelectric effect, and light intensity could be calculated from the amplified current value, and similarly the light pressure could be calculated in accordance with the intensity-pressure relationship of light.
With the development of material science, films with a thickness of nano magnitude have been successfully prepared. For example, metal films with a thickness of 20 nm can be prepared with the vacuum evaporation method proposed in “Nonlinear resistance effect of nano aluminum films” of LI ZhiRui.